Machines for floor maintenance have employed electric motors in which the armature conductors were parallel to the axis of the rotor and the field poles were radial to the axis of the motor. Such motors resulted in a shape having a relatively long axial dimension compared to the radial dimension of the motor. This configuration resulted in a shape lacking conformity with the pad or brush to be driven by the motor. Such motors were of the induction-type motors or the commutated armature type motors with electrical brushes.
Induction type motors generally have low starting torque and the revolutions per minute have been maintained within a limited range. This arrangement has required a reduction drive mechanism. The commutated type motors with electrical brushes produce higher torques and operate over a larger range of revolutions per minute. Generally reduction drive mechanisms are required to reduce the revolutions per minute to desired operating speeds. However, the commutated type motors have short life components, which require frequent replacements. This is particularly recognizable at high speed operations.
Floor maintenance pads are attached to the rotor of a floor machine by a pad holder. Heretofore, the surface of the pad holder containing the pad has been flat. As a consequence thereof, the weight of the machine has been applied substantially evenly across the pad, excepting the area of the pad contiguous with the central hole thereof.
In the U.S. Pat. No. 4,330,897, to Tucker et al., issued on May 25, 1982, for Floor Machine, there is disclosed a machine for floor maintenance with pads. The pads are held by a drive unit having drive tufts made of rigid plastic. The U.S. Pat. No. 4,122,576, to Bevington et al., issued on Oct. 31, 1978, discloses a floor polishing machine in which a pad is driven by an electric motor through a drive plate. By tilting the shaft of the drive plate, a segment of the pad presses harder against the floor than another segment of the pad.
The U.S. Pat. No. 4,125,792, to Schmider, issued on Nov. 14, 1978, for Brushless D-C Motor discloses an axial gap motor which has coreless armature stator windings and a permanent magnet motor. Sensors sense the rotary position of the motor and control switching of current to the respective armature windings.
The U.S. Pat. No. 4,276,490, to Saldinger, issued on June 30, 1981, for Brushless DC Motor With Rare-Earth Magnet Rotor And Segmented Stator discloses a rotor formed with permanent magnets and a stator formed with armature windings. The armature windings are excited by amplifiers of a commutated power source to provide a three phase relationship. Sensors may be provided in lieu of amplifiers to sense the position of the magnets on the rotor for exciting the armature windings.
In the publication, DC Motors Speed Control Servo Systems, by Electra Craft Corporation, published 1980, there is disclosed in pages 6-11 through 6-35 control circuits for brushless d.c. motors.